No stereo sound on headphones through imac

Hi all, just new on the forum a few minutes ago as I am desperately seeking some help.
Just come back from NYC - visisted the apple store and got a nice headphone...Switching it onto my imac back home i just seem to get mono sound out of it. Are there preferences , settings i need to adjust - and if so where ? ( am a new mac user so still finding my way around the system after years and years of windows ...) Thanks for feed back !

I shouldn't imagine you need to.... but go to , system preferences, sound, output, and check that the balance is in the middle.
If that's not the problem, I'd test the headphones on another device, or test other headphones on your Mac.

Thanks , but I did check this
However after some seeking there is / was nothing wrong with the headset !
Eventually I got to the " Universal access preferences" on the mac and found the box " play stereo sound as mono" ticked on the " hearing" tab.
Who could have imagined this... Anyway, found it - solved it. Appreciate your effort though. All the best.

@previous

I have the same problem except, everything is the same except for how you resolved it. I went to universal access like you did but it was already set how it was supposed to be (not mono) yet I still get sound louder in one earphone than the other (right > left). Let me know if either of you know any possible solutions. I know it can't be the headphones b/c I've already tried them on other devices and they work fine. This isn't the first pair of headphones that have had this same problem with this computer either.

6string, you just solved my 'sound problem'... somehow sound balance was off to the right ... THANK YOU ...